Re: [SeaBIOS] [PATCH 3/6] qemu: add bochs-display support

[Gerd Hoffmann]

On Thu, May 31, 2018 at 11:12:14AM -0400, Kevin O'Connor wrote:
> On Thu, May 31, 2018 at 08:33:50AM +0200, Gerd Hoffmann wrote:
> [...]
> > dprintf(1, "bochs-display: using %dx%d, %d bpp (%d stride)\n"
> >        , FRAMEBUFFER_WIDTH, FRAMEBUFFER_HEIGHT
> >        , FRAMEBUFFER_BPP * 8, FRAMEBUFFER_STRIDE);
> > cbvga_setup_modes(lfb_addr, FRAMEBUFFER_BPP * 8,
> >                  FRAMEBUFFER_WIDTH, FRAMEBUFFER_HEIGHT,
> >                  FRAMEBUFFER_STRIDE);
> > writew(dispi + VBE_DISPI_INDEX_XRES,   FRAMEBUFFER_WIDTH);
> > writew(dispi + VBE_DISPI_INDEX_YRES,   FRAMEBUFFER_HEIGHT);
> > writew(dispi + VBE_DISPI_INDEX_BPP,    FRAMEBUFFER_BPP * 8);
> > writew(dispi + VBE_DISPI_INDEX_ENABLE, VBE_DISPI_ENABLED);
> > writeb(vga, 0x20); /* unblank (for qemu -device VGA) */
>
> An additional question - if the mode can be changed why do we only
> change it on startup?  Is the idea that the OS will have a driver
> installed that directly changes modes once the OS starts up?

Yes.  On linux bochs-drm.ko can handle the device.

Also modesetting isn't that easily in real mode due to the registers
being in a 32bit mmio bar.  setup() is fine due to running in big real
mode.

cheers,
  Gerd